Conventionally, as a flow measuring device, there is a device including a housing having a bypass flow passage that guides a part of air (mainstream) flowing in a duct, a temperature sensor for measuring temperature of the air flowing in the duct outside the housing, and a protection cover that is provided integrally with the housing to protect the temperature sensor (see, e.g., JP2010-185793A).
The air flow measuring device is inserted into the duct through an attachment hole formed at the duct so as to be disposed in the duct. When a side facing an opening edge of the attachment hole at the time of the insertion of the device is referred to as a front side of the temperature sensor, and an insertion direction side is referred to as a lower side of the temperature sensor, a protection member has an L-shape in section surrounding the front side and the lower side of the temperature sensor. The protection cover having such a shape prevents contact of the temperature sensor with the duct at the time of the insertion of the device into the attachment hole, and also serves as a protection member that protects the temperature sensor from objects approaching the temperature sensor such as fingers and other members.
However, the protection cover in an L-shape in section has a complicated mold structure at the time of resin-molding. In Japanese Patent No. 3242286, there is described an art whereby a protection wall projecting from a side surface of the housing is provided on a lower side of the temperature sensor to prevent the contact of the temperature sensor with the duct at the time of the insertion into the attachment hole. Nevertheless, this protection wall has an insufficient protective function because its end is located inward of the temperature sensor.